Micromanipulator with piezoelectric movement elements

ABSTRACT

The invention relates to a micromanipulator ( 1, 8, 14, 35 ) which is used to produce a relative movement between said micromanipulator and an object ( 7, 13, 25, 34 ). The micromanipulator ( 1, 8, 14, 35 ) has piezoelectric movement elements ( 3, 10, 15, 16, 17, 43, 44, 45 ) which are provided with end pieces ( 6, 12, 22, 23, 24, 46, 47, 48 ). The inventive micromanipulator is characterized in that the end pieces ( 6, 12, 22, 23, 24, 46, 47, 48 ) are magnetic or can be magnetized.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/EP00/06554 filed Jul. 11,2000 and based upon German national application 199 35 570.3 filed Jul.30, 1999 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a micromanipulator for producing a relativemovement between itself and an object, whereby the micromanipulator haspiezoelectric movement elements which are provided with end pieces.

Micromanipulators of this type are used to effect movement in scanningtunnel microscopes (STM) or scanning force microscopes or atomic forcemicroscopes (SFM or AFM). Here the highest possible degree of precisionis required for the movement of the sensing needle (tunnel tip) relativeto the object to be investigated by the micromanipulator.

BACKGROUND OF THE INVENTION

In DE 36 10 540 C2, a micromanipulator is described in which, for thesupport of the object to be investigated, a multiplicity of movementelements of piezoelectric materials are fastened on a base plate. Themovement elements are so configured that they can effect micromovementsof an object or object holder resting on the movement elements, e.g.translational movements and rotational movements, as well as a tiltingof the object. The described micromanipulator is arranged formicromovement of the object with any optional micromovement.Perpendicular to the object plane, movements are effected only to theextent that they are permitted by the deformation of the piezoelectricmaterials by the applied electrical voltage.

In DE 38 22 504, a further development of the aforedescribedmicromanipulator is disclosed. Ii it the movement elements are arrangedon a part which is movable against the force of a spring relative to thebase plate, whereby via the spring a micromovement of the order ofmagnitude of several tenths of a millimeter is effected perpendicular tothe object plane while maintaining its basically horizontal orientation.A similar effect can be produced with the configuration of amicromanipulator according to DE 38 44 659 A1.

In FIG. 6 of this document an embodiment is disclosed in which themicromanipulator in an inverted arrangement is configured as a runnerwhich extends above the piezoelectric movement elements on an object.The runner can be moved entirely translatorily or rotationally in ahorizontal plane or in a plane tilted thereto at a small angle. With theaid of such a micromanipulator, even larger objects can be analyzedwithout detriment.

In DE 38 44 821 C2, a micromanipulator is disclosed in which themovement elements are provided with end pieces for the apparatus whichare so mounted in axially extending bushings that friction forcesbetween mutually bounding surfaces at end pieces and bushings hinder amovement of the support in the bushing. The frictional forces are sodimensioned that they on the one hand suffice to brace the object or theobject holder and, on the other hand, by application of voltagefunctions to the piezoelectric material achieve a sliding of the endpiece in the bushing in the axial direction. Thus by piezoelectricdeformation the adhesion friction forces between end piece and bushingare eliminated and the relative movement is produced by inertia. In thisconfiguration, the movement elements are perpendicular to the shaping oranalysis plane for the micromovement and the macromovement of the objector object holder is utilized. In any case, the micromovements remainlimited to a fraction of the length of the movement element.

A basic problem in the use of scanning probe microscopes (scanningtunnel microscopes and scanning force microscopes) resides in the factthat in the investigation of certain surface regions on a workpiece, asample must be separated therefrom which contains the surface to beinvestigated. The sample is then introduced into the microscopeapparatus. The separation can only be avoided in those particular casesin which the workpiece itself is very small or in an appropriate shapefor investigation in the microscope apparatus. In many cases the needfor taking a sample prevents microscopic investigation, for example,when the workpiece on objective grounds or because cost should not bedamaged or because of its geometry is not capable of being introducedinto the microscope apparatus as is the case, for example with an engineblock, a bridge girder, etc.

Up to now, no scanning probe microscope or micromanipulator is knownwhich is suitable for the investigation of optional locations on largeimmovable workpieces. This is because of one or more of the followingreasons:

(i) The scanning probe microscope is not functionally suitable becauseof its excess sensitivity with respect to noise and vibration withoutspecial oscillation damping.

(ii) The scanning probe microscope requires the proximity of probe andsample and for the investigation of the sample, a certain sampleorientation.

(iii) The scanning probe microscope does not structurally permit theapproximation of a probe to an optional location of the sample on aworkpiece with the requisite precision and closeness required in thescanning probe microscope.

Thus for scanning probe microscopes of the above described types, allthree of the mentioned reasons are applicable.

Especially the sensitivity identified under (i) of the scanning probemicroscope to noise and vibration is a basic problem in the use of allscanning probe microscopes. Thus the operation of variable temperaturescanning probe microscopes of the above described types (compare Bott eta., “Design Principles of a variable temperature scanning tunnelingmicroscope”, Rev. Sci. Instrumen. 66 (8), August 1995, P. 4135 to 4139)is affected by the boiling of the coolant to a significant degreethrough vibration.

The application force between the object or the object holder with thesample and the microscope or of the runner on the object or the objectholder has been only a result of the intrinsic weight. The applicationforce is only small and gives rise, at the bearing points in thepresence of environmental noise or vibration to relative movementbetween the micromanipulator and object or object holder (compare Behleret al, “Method to characterize the vibrational response of a beetle typescanning tunneling microscope”, Rev. Sci. Instrum. 68 (1), January 1997,P. 124 to 128). To solve this problem, various possibilities have beenproposed in this document, for example, the reduction of the possibilityof introduction of the environmental noise by improved vibrationinsulation or the change in the configuration of the micromanipulator toincrease the application force, e.g. by increasing the weight or by theuse of a magnetic or electrostatic clamping of the microscope andobject. As to how this can be achieved in detail, the document sheds nolight. If the piezoelectric movement elements are loaded, theaforementioned problems are not resolved. The internal resonancefrequency of the movement elements decreases sharply by loading and thusagain gives rise to increased sensitivity of the scanning probemicroscope to environmental noise and vibration.

OBJECT OF THE INVENTION

The invention thus has as its object a micromanipulator of the typementioned at the outset but of reduced sensitivity to environmentalnoise or vibration so that it can also be used at optional locations ona large object without requiring comminution of it.

SUMMARY OF THE INVENTION

This object is achieved in accordance with the invention in that the endpieces are magnetic or magnetizable. With end pieces configured inaccordance with this feature, the application force can be significantlyincreased. To the extent that the end pieces are magnetic, it sufficesthat the object to be investigated—or the object holder—be composed of amagnetizable material or have a magnetizable coating. If the end piecesare only configured to be magnetizable, it is necessary for increasingthe application force that the object itself—or the object holder—bemagnetic. The advantage of the micromanipulator with the configurationaccording to the invention is that the piezoelectric material of themovement elements is not loaded by the increase in the application forcesince the application force increase is exclusively effected between theend pieces of the movement elements and the object or object holder. Asa result there does not arise a reduction in the intrinsic resonance ofthe movement elements. Rather there is an increase in the intrinsicresonance because of the bond with the workpiece. This enables themicromanipulator to be used under normal environmental conditionswithout external vibration damping and in spite of it to obtain a highresolution of better than 1 nm on an optional object. The invention thuspresents especially an improvement for all micromanipulators in thesignificant elimination of vibration or ambient noise or where aninsulation from such detrimental influences is not possible.

The further advantage of the micromanipulator configured in accordancewith the invention is that because of the great adhesive force betweenthe micromanipulator and object—or object holder—the function of themicromanipulator in any optional orientation is ensured and is no longerlimited to a substantially horizontal orientation of the plane of theend pieces (and thus the object). This enables especially themicromanipulator to be operated at any optionally oriented location of alarge object without comminuting it. This feature also enables objectsto be transported in optional directions over macroscopic andstructurally unlimited distances.

To the extent that the end pieces are of magnetic configuration, theinvention provides that the end pieces be comprised at least partly ofmagnetic material. Alternatively, the end pieces can also be comprisedat least partly of magnetizable material and that they be juxtaposedeach with a respective magnet which magnetizes the end piece. For themagnets, permanent magnets or electromagnets can answer.

In a further feature the invention provides that the micromanipulatorhas an object holder which rests upon end pieces and is configured to bemagnetic or magnetizable. Thus the object holder can be applied to anobject or a part thereof. Such an object holder is concerned with verysmall workpieces which should be investigated. When the end pieces aremagnetic, it suffices for the object holder to be comprised of amagnetizable material. If the end pieces are only magnetizable, theobject holder should itself be magnetic to increase the applicationforce between end pieces and object holder. The magnetic characteristicsof the object holder can be obtained by means of permanent magnets orelectromagnets.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in greater detail in the drawing based uponexamples. The drawing shows:

FIG. 1 a vertical section through a movement element of amicromanipulator according to the invention;

FIG. 2 a micromanipulator for flat objects;

FIG. 3 a longitudinal section through a movement element of amicromanipulator according to FIG. 2;

FIG. 4 a micromanipulator as a runner on an object in a perspectiveview; and

FIG. 5 a scanning tunnel microscope with an object.

SPECIFIC DESCRIPTION

The micromanipulator partly shown in FIG. 1 has a base plate 2 fromwhich a movement element 3 extends vertically upwardly. Apart from thismovement element, two further movement elements, here not shown butoriented in parallel, as well as a scanning element, likewise arrangedin a parallel orientation and centrally of the movement element 3 areprovided so that the micromanipulator in its basic configurationcorresponds to the micromanipulators like those of FIG. 1 of DE 36 10540 C2, DE 38 22 504 C2 and DE 38 44 659 A1.

The movement element 3 has a small tube 4 of piezoelectric material,whose lower end is recessed in the base plate 2. In the region of theupper end, a disk-shaped magnet 5 is inset and is magnetized in thedirection of the longitudinal axis of the small tube 4.

On the upper side of the magnet 5 a hemispherically-shaped end piece 6is glued and is composed of a magnetizable material. This end piecerests against the underside of the object 7 to be investigated and whichis also composed of a magnetizable material or is provided at least onits underside with a coating of such material. Because of themagnetization of the end piece 6 by the magnet 5, the application forceof the object 7 on the end piece 6 is increased by up to two orders ofmagnitude. Since the remaining movement elements are identicallyconfigured, this also applies for these movement elements. The smalltube 4 is provided with suitable electrodes so that a relative movementbetween the small tube 4 and the magnet 5 can be effected utilizing theteachings of DE 38 44 821 C2 to produce micromovements with respect tothe object 7.

The micromanipulator 8 shown in FIG. 2 has a vertically arranged baseplate from which a total of 8 movement elements—for example designatedat 10—project horizontally.

As FIG. 3 indicates, the movement elements 10 here are small tubes 11 ofpiezoelectric material. In the free ends of the tubes 11, end pieces 12with hemispherical tips are inserted which function as magnets.

A plate-shaped object 13 rests against the movement elements 10 and iscomposed of a magnetizable material or has a magnetic coating or guide.With the aid of the movement elements 10, the object 13 can havemicromovements imparted to it in optional directions, particularly inthe vertical direction. To the extent that FeNeB magnets with a diameterof 2 mm and a length of 1.5 mm are used, retaining forces per contactpoint of about 0.5 N can be produced. The total holding force F_(H) isgiven by the addition of the retaining forces of the individual contactpoints. The maximum vertical transportable load with a weight F_(G) canbe obtained by the Armontonic law and amounts for an adhesion frictioncoefficient μ_(H) typically to F_(G)≈μ_(H)F_(H), i.e. several tenths ofthe magnitude of the summed adhesion forces.

FIG. 4 shows a further micromanipulator 14 in the form of a runner. Ithas three movement elements 15, 16, 17, arranged in a triangle andprojecting vertically from a base plate 18. The movement elements 15,16, 17 are identical with the movement elements 10 in themicromanipulator 8 according to FIGS. 2 and 3 and have each,respectively a small tube 19, 20, 21 in whose free ends respective endpieces 22, 23 and 24 are inset and are formed as magnets.

The micromanipulator 14 bears on the underside of an object 25 ofmagnetizable material and the retaining force generated by the endpieces 22, 23 and 24 is greater than the weight of the magnetmanipulator 14. It can thus be moved over the object 25 in any optionaldirection in space. Thus the object 25 need not necessarily be planar.It is sufficient when the local radii of curvature of the object 25 isat least of the order of magnitude of the spacing of the movementelements 15, 16, 17. Such a micromanipulator can thus be displaced inpipes.

In FIG. 5, a scanning tunnel microscope 26 has been illustrated whichcan be used for optional sample locations on large immovable objectswhich are unsuitable for the removal of samples therefrom. The scanningtunnel microscope 26 has a housing 28 which is composed of a cylindersegment 29 of transparent material and a plug plate 30 closing one sideof it. On the object side, the housing 28 is closed by a ramp ring 31which is threaded onto the cylinder segment 29 by a screw thread 32 to astop 33. The ramp ring 31 is attached, for example by gluing, byadhesion or by a screw thread connection with an object 34.

In the housing 28 there is a micromanipulator 35 of the runner typewhose base plate 36 initially is retained by means of locking screws 37,38, 39 on the cylinder segment 29 and in which the locking screws 37, 38and 39 extend through the cylinder segment 29 and engage in lockingholes 40, 41, 42 of the base plate 36. From the side of the base plateturned toward the object 34, movement elements 43, 44, 45 project, themovement elements having their free ends provided with magnetic endpieces 46, 47, 48. They are configured exactly like the movementelements 10, 15, 16, 17 of the micromanipulators 8, 14, according toFIGS. 2-4. From the middle of the base plate 36 projects a tunnelmicroscope tip 49 in the direction of the object 34 which serves for theanalysis.

The use of the scanning tunnel microscope 26 is effected in thatinitially the ramp ring 21 is applied to the object 34. Then the housing28 is screwed onto the ramp ring 31 until it reaches the stop 33,whereby the micromanipulator 35 is initially fixed via the lockingscrews 37, 38, 39. After removal of the locking screws 37, 38, 39, themagnetic end pieces 46, 47, 48 effect a movement of the micromanipulator35 until the end pieces 46, 47, 48 lie against the ramp ring 31. Byapplication of suitable selected electrical pulses to the piezoelectricmaterial of the movement elements 43, 44, 45, a rotation of themicromanipulator is effected counterclockwise to result, because of theshapes of the ramps of the ramp ring 31, in an approximation of thetunnel microscope tip 49 to the object 34, until the tunnel microscopetip lies in the requisite range for the measurement. Also by theapplication of suitably selected electrical pulses to the movementelements 43, 44, 45, a translation of the micromanipulator 35 can beeffected and thus the desired location of the object 34 can be broughtinto the proximity of the tunnel microscope tip 49 and thus in the imagefield of the scanning tunnel microscope 26. The function of the tunnelmicroscope 26 does not, therefore, depend upon its orientation which canbe dependent upon the orientation of the location to be investigated onthe object 34.

The transparency of the cylinder segment 29 enables it to be located onthe site of the object 34 to be investigated initially by means ofoptical microscopy and then controlled by the movement of themicromanipulator to bring that site into the image region of thescanning tunnel microscope 26. The electrical energy required for theactuation of the movement elements 43, 44, 45 is supplied to the plugplate 30 via thin wires which have, for example, been indicated at 50.The measured signal is initially passed through a metallic shieldingtube 51 to an integrated preamplifier 52 before it is also delivered tothe plug plate 30. From the plug plate 30 the scanning tunnel microscope26 can be connected with the required measurement circuitry. Thescanning tunnel microscope 26 has in the described example a length ofabout 12 cm and a diameter of about 4 cm.

Instead of the ramp ring, the approximation to the site to be exploredon the object 34 can be effected by an inertial drive as is disclosed inDE 38 44 821 C2. In this case, a smooth ring without ramps suffices. Inaddition, the described arrangement can be used also as a scanning forcemicroscope by replacement of the tunnel microscope tip 48 by a needlesensor corresponding to that of DE 195 13 529 A1 and then can be usedalso for the investigation of electrically nonconducting workpieces.

What is claimed is:
 1. A micromanipulator for producing a relativemovement between the micromanipulator and an object which has a surfaceat which the object is magnetically attractable, said micromanipulatorcomprising: a support; at least three piezoelectric movement elementsextending from said support substantially perpendicular to said surfaceand having respective end pieces in continuous contact with said surfaceat spaced-apart locations on said surface and constituting the exclusivecontacts of said manipulator with said object, said end pieces beingmagnetic or magnetizable to maintain the contact of said end pieces withsaid surface magnetically during relative movement of themicromanipulator and the object; and means for energizing saidpiezoelectric movement elements to effect relative movement of saidmicromanipulator and said object without loss of contact between saidend pieces and said surface.
 2. The micromanipulator defined in claim 1wherein said end pieces are hemispherical and engage said surfacesubstantially with point contact.
 3. The micromanipulator defined inclaim 2 wherein said end pieces are at last partly composed of magneticmaterial.
 4. The micromanipulator defined in claim 2 wherein said endpieces are at last partly composed of magnetizable material and each ofsaid end pieces is juxtaposed with a magnet forming part of therespective movement element.
 5. The micromanipulator defined in claim 2,further comprising an object holder which is magnetic or magneticallypermeable interposed between said elements and said object and formingsaid surface.
 6. A scanning probe microscope comprising: amicromanipulator for producing a relative movement between themicromanipulator and an object which has a surface at which the objectis magnetically attractable, the micromanipulator comprising: a support,at least three piezoelectric movement elements extending from saidsupport substantially perpendicular to said surface and havingrespective end pieces in continuous contact with said surface atspaced-apart locations on said surface and constituting the exclusivecontacts of said manipulator with said object, said end pieces beingmagnetic or magnetizable to maintain the contact of said end pieces withsaid surface magnetically during relative movement of themicromanipulator and the object, and means for energizing saidpiezoelectric movement elements to effect relative movement of saidmicromanipulator and said object without loss of contact between saidend pieces and said surface; and a scanning microscope tip between saidelements and juxtaposed with said object.
 7. The scanning probemicroscope defined in claim 6 wherein the micromanipulator has amagnetic or magnetically permeable object holder resting against saidobject and forming the surface engaged by said end pieces.